The present invention relates generally to the coating of substrates and, more particularly, to systems and methods for coating substrates in the fabrication of semiconductor devices using ink jet technology.
Spin coating is used to form films over substrates in the fabrication of a variety of devices. For example, in the fabrication of semiconductor devices, films of photoresist materials, anti-reflective materials, and low dielectric constant materials (sometimes referred to as xe2x80x9clow k materialsxe2x80x9d) are spin coated over the surface of semiconductor wafers. In a typical spin coating operation in which a photoresist coating is applied over the surface of a wafer, photoresist fluid is applied on the surface of the wafer and the wafer is spun at high speeds in a spin bowl. The centrifugal force caused by the rotation of the wafer causes the photoresist fluid to spread over the surface of the wafer and form a film. Excess photoresist fluid that spins off the surface of the wafer drains from the spin bowl and is collected in a stationary drain bowl disposed below the spin bowl.
Unfortunately, the formation of films over substrates, e.g., semiconductor wafers, by spin coating suffers from at least five significant drawbacks. First, spin coating consumes a large quantity of the material being applied on the surface of the substrate. In a typical spin coating operation, roughly 95% of the material initially applied on the surface of the substrate is spun off during the operation. Second, the excess material generated during the spin coating operation must be disposed of in accordance with relatively expensive waste management procedures to minimize the impact on the environment. Third, spin-coated wafers typically require edge bead removal to provide a clean edge area that can be gripped by robotic wafer handling equipment. The solvents used in edge bead removal processes also must be disposed of in accordance with waste management procedures. Fourth, spin-coated wafers typically require backside rinsing to remove contaminants from the backside of the wafer. Fifth, spin coating does not afford a wide range of film thickness control in that the viscosity of a material limits the minimum film thickness and the maximum film thickness that can be obtained at a reasonable coating uniformity. Consequently, it may not be possible to obtain a specified film thickness for a given material by spin coating.
In view of the foregoing, there is a need for a method for coating substrates that efficiently uses the material being applied on the substrate, does not require waste management, edge bead removal, or backside rinsing, and provides a wide range of film thickness control.
Broadly speaking, the present invention fills this need by providing a system and method for coating substrates using ink jet technology. In the system and method, drops of coating material are dispensed from a print head onto the substrate.
In accordance with one aspect of the present invention, a method for coating a substrate is provided. In this method, a print head is disposed over a surface of a substrate, which may be a semiconductor, an insulator, or a conductor. A first drop of a coating material is dispensed from the print head to form a first dot of the coating material on the surface of the substrate. A second drop of the coating material is dispensed from the print head to form a second dot of the coating material on the surface of the substrate. The second dot overlaps the first dot to form a homogeneous film of the coating material on the surface of the substrate. The degree to which the dots overlap may be varied between having the dots just touch one another and having just less than 100% overlap, i.e., having the dots formed substantially on top of one another.
In one embodiment, the substrate is comprised of a material selected from the group consisting of silicon, gallium arsenide, silicon germanium, glass, aluminum, and copper. In one embodiment, the coating material may be a polymer, a solvent media containing a solute, an aqueous media containing a solute, and a dispersed colloidal suspension. Exemplary coating materials include low dielectric constant materials, photoresist materials, and antireflective coating materials.
In accordance with another aspect of the present invention, a method for applying a coating material on a substrate is provided. In this method, a print head is disposed over the substrate, and drops of a coating material are controllably dispensed from the print head to form a wide area film on a surface of the substrate. In one embodiment, the substrate may be a semiconductor wafer. In one embodiment, an ultraflat wide area film may be formed on the surface of the substrate.
In accordance with yet another aspect of the present invention, a system for coating a semiconductor wafer is provided. This system includes a housing, and a chuck for supporting a semiconductor wafer is disposed in the housing. A print head is movably disposed in the housing above the chuck such that the print head is movable in first and second dimensions over the chuck. A source of a coating material is coupled to the print head. A digital signal processor provides control signals for controlling process parameters for dispensing drops of the coating material from the print head and provides control signals for controlling a position of the print head relative to the chuck.
In one embodiment, the process parameters for dispensing drops of the coating material from the print head and the position of the print head relative to the chuck may be controlled to form a wide area film on a surface of a semiconductor wafer being supported on the chuck. In one embodiment, the first and second dimensions define a plane over the chuck, and the print head is movable in the plane. In one embodiment, the system further includes a maintenance station for performing maintenance operations on the print head.
In one alternative embodiment of the system, the chuck is movably disposed in the housing below the print head such that the chuck is movable in first and second dimensions under the print head. In this alternative embodiment, the process parameters for dispensing drops of the coating material from the print head and the position of the print head relative to the chuck may be controlled to form a wide area film on a surface of a semiconductor wafer being supported on the chuck. In one embodiment, the first and second dimensions define a plane under the print head, and the chuck is movable in the plane.
In another alternative embodiment of the system, the chuck is movably disposed in the housing such that the chuck is movable in a first dimension, and the print head is movably disposed in the housing above the chuck such that the print head is movable in a second dimension. In this alternative embodiment, the process parameters for dispensing drops of the coating material from the print head, the position of the chuck relative to the print head in the first dimension, and the position of the print head relative to the chuck in the second dimension may be controlled to form a wide area film on a surface of a semiconductor wafer being supported on the chuck. In one embodiment, the first dimension is an X dimension and the second dimension is a Y dimension.
The system and method for coating substrates of the present invention provide a number of significant advantages relative to spin coating. These advantages include conserving expensive coating material (because the print head dispenses coating material onto only those portions of the substrate where film coverage is desired), eliminating the need for edge bead removal (because a film is not formed on the edge exclusion area), eliminating the need for waste management (because coating material is not wasted and no edge bead removal, which uses solvents, is needed), and eliminating the need for backside rinsing (because coating material is not deflected onto the backside of the substrate during the coating operation). The system and method of the present invention are further advantageous because they enable the pattern, thickness, thickness profile, and smoothness of a film to be modulated over the substrate.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.